This invention relates to a wheel suspension for an axle of a motor vehicle, particular for a McPherson front axle.
A wheel suspension is known from German Patent Document DE 36 16 005 C2 in which a lower transverse control arm is swivellably connected by means of its one end to the vehicle frame and is swivellably connected by means of its other end with a steering knuckle. A strut which extends approximately in the longitudinal direction is rigidly connected with the transverse control arm, the free end of the strut being elastically supported on the vehicle body.
Furthermore, a wheel suspension is known from German Patent Document DE 32 00 855 A1 in which a strut is connected in an articulated manner with a transverse control arm.
It is an object of the invention to provide a wheel suspension for an axle of a motor vehicle comprising a McPherson strut which, when peripheral forces act upon the wheel, ensures a targeted elastokinematic wheel position change which assures advantageous influences on the vehicle handling characteristics during cornering and straight-ahead driving.
According to the invention, this object is achieved by means of a wheel suspension for a motor vehicle comprising:
a wheel carrier for carrying a wheel rotatable about a wheel spin axis, PA1 a McPherson spring strut springingly supporting the wheel carrier at a vehicle body, PA1 a steering gear tie rod extending below the wheel spin axis and connected to the wheel carrier, PA1 a transverse control arm connected to the wheel carrier by a first joint connection and connected to a vehicle frame part by a second joint connection, and PA1 a tension strut connected pivotably to the transverse control arm by a third joint connection and to a vehicle frame part by a fourth joint connection.
wherein the transverse control arm with the connected tension strut is arranged in an approximately horizontal plane and extends below the wheel spin axis approximately in a wheel center transverse plane, the tension strut extending at an angle diagonally with respect to a vehicle longitudinal center axis, and
wherein the transverse control arm is spaced a distance in each of the perpendicular and longitudinal direction of the vehicle with respect to the tie rod and is disposed behind the tie rod with respect to the vehicle driving direction.
Principal advantages achieved by means of the invention are that the wheel suspension, as a result of the positioning of the transverse control arm with the tension strut with respect to the tie rod of the steering gear and of the positioning of the McPherson strut with respect to the transverse control arm, a targeted elastokinematic wheel position change is achieved while forces act upon the wheel, whereby the vehicle handling can be advantageously influenced in the case of braking and driving forces as well as in the case of a longitudinal springing. It is advantageous that, as a result of the wheel suspension according to the invention, the wheel is adjusted in the toe-out direction during braking in a curve.
Thus, the transverse control arm together with the connection tension strut is arranged in an approximately horizontal plane, the transverse control arm extending below the wheel spin axis approximately in a wheel center transverse plane. The tension strut is connected with the transverse control arm by way of an elastic bearing, this tension strut being arranged at an angle diagonally with respect to a longitudinal center axis of the vehicle. In the perpendicular and longitudinal direction, the transverse control arm is disposed at a distance from the tie rod.
In order to achieve an excursion of the transverse control arm, this transverse control arm and the tension strut are each pivotally connected by way of an elastic bearing held on a subframe. The bearing of the tension strut has radial recesses which are arranged in the axial direction of the tension strut. As a result, in the loading direction, which corresponds to the axial direction of the tension strut, a soft characteristic of the bearing is achieved. The elastic bearing of the tension strut with the radial recesses may also be arranged in the transverse control arm. In contrast, the body-side bearing of the transverse control arm is constructed to be radially stiffer, on the whole.
For achieving approximately identical lever conditions on the wheel suspension, the distance between the two body-side bearings of the transverse control arm and of the tension strut are constructed corresponding to the length of the transverse control arm between its two bearings. The connection bearing between the tension strut and the transverse control arm permits a movement and, in the radial direction, has a softer characteristic than the bearing of the transverse control arm. For the connection with the connection bearing on the transverse control arm, the tension strut has a fork head which reaches over the bearing from both sides.
The body-side bearing of the tension strut with its radial recesses essentially contributes to achieving a longitudinal springing. In the case of the longitudinal springing, the wheel can move toward the rear and toward the front--with respect to the driving direction--about an imaginary correcting pole. This pole is formed by the setting of the transverse control arm with respect to the tie rod--in the top view. The pole is situated on the interior side of the wheel whereby the wheel can adjust in the toe-out direction during a movement toward the rear. In the case of a longitudinal springing toward the front, the wheel moves into the toe-in direction. A body-side bearing is used as a pivot for the transverse control arm.
A steering axis is formed between the body-side bearing point of the McPherson strut and the bearing point of the transverse control arm on the wheel carrier. This steering axis has a point of intersection in the wheel contact plane and outside the track gauge. The point of intersection of this steering axis is arranged in front of the wheel center transverse plane--with respect to the driving direction--and crosses the wheel spin axis on the interior side of the wheel. As a result of the position of the steering axis with respect to the perpendicular wheel center longitudinal plane, a lever arm is formed at the level of the wheel spin axis. In the case of driving forces, this position of the steering axis causes a moment in the wheel center, whereby the tie rod is stressed by pressure and the transverse control arm is stressed by tension. Corresponding to the defined elasticity of the body-side elastic bearing of the transverse control arm in the radial directions, in the case of driving forces, the wheel is therefore adjusted in the toe-in direction.
When braking forces act upon the wheel, a wheel position change is achieved in the toe-in direction, for the purpose of which, on the one hand, the steering axis has a negative steering offset and, on the other hand, the tie rod--viewed from the rear--extends from the pivotal connecting point on the steering gear to the wheel-carried-side bearing sloped at an angle toward the road and it has a shorter construction with respect to the transverse control arm. This causes a wheel position change in the toe-in direction when the caster angle of the steering axis is reduced under the effect of braking forces.
The position of the steering axis is designed such with respect to the wheel that a larger lever arm is created in the wheel center than in the wheel contact surface so that, in connection with the bearings of a defined elasticity on the subframe or on the vehicle body, the wheel position change in the toe-in direction as a result of the driving forces of a wheel position change in the toe-in direction can be superimposed, in addition, by a longitudinal springing. So that the toe-in change is kept within limits, the body-side bearing on the tension strut is provided which such a characteristic curve that the longitudinal springing toward the front in the driving direction remains low. This improves the straight running of the vehicle.
The caster angle of the steering axis can be changed corresponding to the use of a power steering system or a manual steering system. For this purpose, the upper bearing point of the spring strut is adjusted in the driving direction so that, in the case of power steering, a larger caster angle can be adjusted and, in the case of manual steering, a smaller caster angle can be adjusted.
So that the holding of the bearing is simplified and the costs of the wheel suspension on the vehicle are minimized, the transverse control arms, the wheel carriers and the bearing as well as the tension struts for the front axle as well as for the rear axle of a vehicle have the same dimensions.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.